THE campaign to keep Britain inside the EU is to formally launch today with a warning that an exit would be a "leap in the dark" and cost every household thousands of pounds.

Former Prime Ministers Gordon Brown, Tony Blair and John Major are set to be unveiled as board members of the Britain Stronger in Europe group, which will campaign for an 'in' vote in the referendum that has been promised by 2017.

The politicians, who also include Labour MP Chuka Umunna, Green MP Caroline Lucas and the former Highland MP Danny Alexander, will be joined by figures including former chief of the general staff Sir Peter Wall, West Ham United vice-chairwoman and Apprentice star Karren Brady, and June Sarpong, a panellist on ITV's Loose Women.

It comes as Nicola Sturgeon once again cited the EU referendum as a potential trigger for a second vote on Scottish independence, saying that if Scotland voted to remain but the UK as a whole opted to leave demand would become "perhaps be unstoppable".

The businessman Lord Rose, the former Marks and Spencer boss, is set to kick off the Britain Stronger in Europe campaign at an event in London today when he is expected to repeatedly brand those who want to leave the EU as "quitters" and reject claims a vote for an exit is patriotic.

Lord Rose, who will chair the campaign, will add: "Make no mistake: I am part of this campaign because I believe that we are stronger, better off and safer inside Europe than we would be out on our own.

"To claim that the patriotic course for Britain is to retreat, withdraw and become inward looking is to misunderstand who we are as a nation. I will not allow anyone to tell me I'm any less British because I believe in the strongest possible Britain for business, for our security and our society."

He will cite CBI estimates that the benefits of trade, investment, jobs and lower prices mean membership is worth £3,000 per year on average to every UK household.

"When you consider that our annual contribution is equivalent to £340 per household, our contribution to the EU is an investment on which British families get a 10-to-one return," he will say.

However, those who back Britain leaving the EU claimed their case had been boosted by reports that David Cameron had drawn up a four-point plan of key demands that he would make as part of a renegotiation of the UK's membership ahead of the vote.

They include explicit statements making it clear that the EU is a "multi-currency union" and that Britain will be exempt from the founding principle of "ever closer union."

However, there is no mention of an opt-out of the free movement of people across the EU, which those who back an exit believe will prove a crucial factor.

UKIP leader Nigel Farage said: "What the British government is asking for, frankly, is nothing. There is no renegotiation."

He also suggested that Boris Johnson, the Tory MP who is stepping down as Mayor of London next year, could be persuaded to take a prominent role in the campaign to leave the EU.

Mr Johnson has so far been careful to support Mr Cameron's position of waiting to see the outcome of the current renegotiation before taking sides, but many believe his private views are more hardline.

"We might just get him," Mr Farage said. "We might just get him and he is a recognisable figure. That would be good news."